1. Field of the Invention
The present invention relates to an electro-optical device of the type driven by an active matrix, as well as to the method of producing such an electro-optical device. More particularly, the present invention pertains to a technical field of an electro-optical device having a conductive layer which serves to provide excellent electrical connection between pixel electrodes and pixel-switching thin film transistors (referred to as xe2x80x9cTFTxe2x80x9d, hereinafter), and also to a method of producing the electro-optical device.
2. Description of Related Art
Hitherto, an electro-optical device of the type driven by a TFT active matrix has a TFT array substrate on which numeral scanning lines and data lines which run in orthogonal directions in a crossing manner are arranged. Numerous TFTs disposed at the points where the scanning lines and data lines cross each other are also arranged. Each TFT has a gate electrode connected to one of the scanning lines and has a semiconductor layer, the source region of which is connected to a data line, while the drain region of the semiconductor layer is connected to the pixel electrode.
The source region, the drain region, and an intervening channel region therebetween are constituted by a semiconductor layer formed on a TFT array substrate. The pixel electrode has to be connected to the drain region of the semiconductor layer, across the laminate structure including the scanning line, capacitance line, data line and a plurality of inter-layer insulation films which serve to electrically isolate these lines from one another. The interlayer distance between the semiconductor layer of the laminate structure and the pixel electrode is as long as 1000 nm or greater, particularly in the case of a positive stagger-type having a top-gate structure, in which a gate is provided on the semiconductor layer formed on a TFT array substrate, or in case of a coplanar-type polysilicon TFT. This makes it difficult to form a contact hole through which the semiconductor layer and the pixel electrode are to be electrically connected to each other. More specifically, a greater depth of etching correspondingly impairs the etching precision, posing a risk of the semiconductor layer being undesirably penetrated and perforated, although the etching has to be stopped upon reaching the semiconductor layer. It is therefore extremely difficult to form such a deep contact hole by a dry etching process alone. One solution is to use both dry etching and wet etching in combination, but such a solution inevitably enlarges the diameter of the contact hole due to the use of the wet etching process, making it difficult to lay out necessary wiring and electrodes in restricted areas available on the substrate.
Under this circumstance, a currently developed technique employs, when achieving electrical connection between a data line and a source region via a contact hole formed in an interlayer insulating film formed on the scanning lines and leading to the source region, a contact hole formed in this inter-layer insulating film and reaching a drain region, a relaying conductive layer generally referred to as a barrier layer and formed on the interlayer insulating film and constituting the same layer as the data line, an additional interlayer insulating film formed on the data line and the barrier layer, and a contact hole formed in the additional inter-layer insulating film and extending from a pixel electrode to the barrier layer, whereby the pixel electrode is connected to the drain region.
In the meantime, a multi-plate-type color projector has been developed which incorporates three units of electro-optical devices such as a liquid crystal display device of the type described above, the three units respectively serving as a red (R) light valve, a green (G) light valve and a blue (B) light valve. For instance, as shown in FIG. 20, the three units of electro-optical devices 500R, 500G and 500B individually perform optical modulation so as to produce light rays of three colors which are then synthesized by a prism 502 to form composite light rays which are then projected on a screen. The synthesis of light rays by the prism 502 involves a problem in that the green light G is not reflected by the prism 502 while the red R and blue B light rays are by the prism 502. Consequently, the green light G undergoes turns of a number which is smaller by one than the number of turns sustained by the red and blue light rays R and B. Obviously, this problem occurs when the optical system is arranged such that the R light or the B light, rather than the G light, pass through the prism without being reflected. The same problem is encountered also when the light rays of the three colors are synthesized into the projected light by means of an optical element used as a substituent for the prism 502, e.g., a dichroic mirror. In this occasion, the electro-optical device 500G for the green color light rays is arranged to cause inversion of image signals from left to right and vice versa by a suitable means, and is driven in such a manner that the scanning direction is reversed to that employed in the electro-optical devices 500R and 500B, thus displaying an inverted image.
The electro-optical devices of the kind described is now facing an increasing demand for higher quality of the displayed images. To meet such a demand, critical factors are higher degree of definition or resolution of the image display area or implementation of micro-fine pixel pitch, as well as a high pixel aperture ratio, i.e., to increase in each pixel the ratio of the light-transmitting aperture area to the non-aperture area which blocks light rays. Implementation of micro-fine pixel pitch, however, poses another problem: namely, since the production technique limits refining of geometric factors such as electrode size, line width and contact-hole diameter, the pixel aperture ratio is undesirably reduced when the pixel pitch is made smaller, as a result of increase of the ratio of the area occupied by the lines, electrodes and so on.
Another problem accompanying the micro-finer pixel pitch is as follows. From the view point of production technique, there also is a limit in the reduction of thicknesses of the TFTs and conductive layers such as those serving as data lines, scanning lines and capacitance lines, as well as thicknesses of intervening inter-layer insulation films. Consequently, the size of a step or height difference appearing on the surface of each pixel electrode, between an area where a line or an element is formed and an area devoid of such line and element, is increased as a matter of comparison with other dimensions. Rubbing of an oriented film having a step generates a liquid crystal disclination region. The above-mentioned relative increase of the step height correspondingly increases the area of such disclination region. Consequently, the disclination region protrudes out of the non-aperture region which surrounds the aperture region of each pixel in a manner like a grating. A solution to this problem might be to cover and conceal the entire disclination region by a light-shield film formed on a counter substrate. Such a solution, however, excessively reduce the area of the aperture region in each pixel, thus posing another problem.
Experiments and studies made by the present inventor proves that the location and extent of disclination caused by the presence of a step on the pixel electrode surface largely depend on the direction of rubbing. It is assumed here that a TN (Twisted Nematic) liquid crystal is used. In such a case, when the TN liquid crystal has clockwise twisting direction as viewed from the counter substrate, rubbing performed in the directions of scanning lines and data lines causes a greater disclination region to appear at the right end portion of the aperture region of each pixel, as a result of the presence of a step on the pixel electrode surface. Conversely, when the TN liquid crystal has counterclockwise twisting direction as viewed from the counter substrate, rubbing causes a greater disclination region to appear at the left end portion of the aperture region of each pixel, as a result of the presence of a step on the pixel electrode surface. Such a disclination having directivity may not be recognizable in a single unit of electro-optical device, but may become noticeable in a multi-plate-type color projector which projects light rays synthesized from the light rays of three different colors produced by three units of electro-optical device. More specifically, the color projector synthesizes three different colors modulated by the respective units electro-optical device, wherein two (units 500R and 500B of FIG. 20) of the units have the same tendency of generation of disclination regions, while the remainder (unit 500G) has the opposite tendency. In this case, the disclination may be locally superimposed and enhanced at a certain location on each pixel to an extent which is highly conspicuous to eyes. In particular, production of a multi-plate-type color projector, employing three units of electro-optical device having a very fine pixel pitch, suffers from a very high rate of production of defective products. Similarly, a multi-plate-type color projector having three units of electro-optical device having a very fine pixel pitch suffers from very heavy deterioration of the image due to disclination attributable to the presence of a step on the surface of each pixel electrode. This makes it extremely difficult to display high-quality image.
The aforementioned technique which uses a barrier layer, it is necessary that at least two contact holes be formed in the non-aperture region, in order to achieve electrical connection between the drain region and the pixel electrode of each pixel. Such two contact holes inevitably produce a plurality of dents or steps on the surface of the pixel electrode overlying these contact holes. Various planarization techniques are usable to remove such dents or steps, but such a measure undesirably complicates the production process and raises the cost of production. Moreover, it impossible to planarize the portion of the pixel electrode surface formed of, for example, an ITO (Indium Tin Oxide) film and overlying a second contact hole that is directly connected to the pixel electrode, although other interlayer insulating films and underlying layers may satisfactorily planarized. Consequently, disclination of liquid crystal inevitably appears at a certain location of each pixel, as a result of formation of dents and steps in the pixel electrode surface, due to the presence of a plurality of contact holes. Alternatively, it is necessary to reduce the area of the aperture region.
In view of the foregoing, it is an object of the present invention to provide an electro-optical device, as well as a method of producing the same, which despite a very fine pixel pitch effectively suppresses undesirable effect of dents and steps formed on each pixel electrode surface due to presence of a plurality of contact holes interconnecting a semiconductor layer and the pixel electrode, thus realizing a high aperture ratio of each pixel and, at the same time, high quality of displayed images.
In order to solve the problems described heretofore, the present invention provides an electro-optical device, which may consist of a substrate on which are formed a plurality of scanning lines, a plurality of data lines, thin-film transistors and pixel electrodes arranged at positions corresponding to the points where the scanning lines and data lines cross each other; and at least one conductive layer electrically connected between a semiconductor layer constituting the thin-film transistor and the pixel electrode, wherein a first contact hole for providing electrical connection between the pixel electrode and the conductive layer is formed in symmetry with respect to two adjacent data lines when viewed in plan.
In accordance with these features of the present invention, the first contact hole for providing electrical connection between the pixel electrode and the conductive layer is formed in symmetry with respect to two adjacent data lines when viewed in plan. The expression xe2x80x9cposition symmetrical with respect to two adjacent data linesxe2x80x9d means, if only one first contact hole exists, the position which is midst between two data lines and, if there are two first contact holes, two positions which are line-symmetry with each other with respect to the central axis line of the region between the two adjacent data lines. Thus, various positions are defined by this expression depending on the number of the second contact holes. The positions symmetrical with respect to two adjacent data lines usually conform with two positions that are symmetrical with each other with respect to the axis line of the pixel aperture extending in the direction of the data line. However, in some cases, the central axis line of the pixel aperture extending in the direction of the data lines cannot definitely be determined unless the pixel aperture has such a configuration as square or rectangular. Thus, the positions symmetrical with respect to two adjacent data lines do not always coincide with the above-mentioned two positions. The first contact hole reaches the pixel electrode and, therefore, dents and steps are more or less caused to appear on the surface of the pixel electrode, at a position where the first contact hole exists, insofar as the presently available production technique is used. Unlike planar portions, the portion where such dents and steps exist causes various undesirable effect on the electro-optical substance, such as disclination of the electro-optical substance after a treatment such as rubbing effected on an alignment film formed on the pixel electrode. In accordance with the present invention, however, the dents and steps in each pixel corresponding to the first contact hole appear at positions symmetrical with respect to the two adjacent data lines, because the contact hole is formed at the position symmetrical with respect to these two adjacent data lines. It is assumed here that a rubbing treatment is effected on the alignment film formed on the pixel electrode, both in the direction for clockwise TN liquid crystal and in the direction for counterclockwise TN liquid crystal. In the present invention, for the reason stated above, any defect of the electro-optical substance due to the presence of the dents and steps on the pixel electrode surface appears in the constant and same tendency, regardless of the rubbing direction, in each and all pixels. It is therefore possible to avoid a risk conventionally encountered with the multi-plate type color projector having a plurality of units of the electro-optical device having different directions of distinctive vision (see FIG. 20), i.e., the risk that defects may be enhanced at certain locations due to superposition. In a more general sense, the dents and steps on the pixel electrode surface of each pixel caused by the presence of the first contact hole do not deviate from the center in either direction along the scanning line. Therefore, any unevenness of display having directivity in the direction of the scanning line is prevented from appearing on the entire image display area. Thus, the requirement of the position being symmetrical with respect to the data lines is sufficiently met if the symmetry is achieved to such an extent that generation of display unevenness having directivity in the direction of the scanning lines is substantially eliminated.
In accordance with the present invention, a second contact hole arranged between the conductive layer and the semiconductor layer for providing electrical connection between the conductive layer and the semiconductor layer is formed in symmetry with respect to two adjacent data lines when viewed in plan.
According to this feature of the invention, the drain region of the semiconductor layer and the conductive layer are electrically connected to each other through the second contact hole. It will be appreciated that each of the contact holes can have a diameter smaller than that of a single, continuous, long contact hole which is used to provide electrical connection between the pixel electrode and the drain region. More specifically, the etching precision is impaired when the depth of the contact hole increases. In order to prevent penetration of the thin semiconductor layer, it is necessary to set up the etching process such that dry etching which enables formation of a contact hole of a small diameter be stopped midway the etching process and be substituted by wet etching which progressively proceeds to reach the semiconductor layer. This wet etching having no directivity inevitably increases the diameter of the contact hole. In contrast, in this embodiment, the electrical connection between the pixel electrode and the semiconductor layer is achieved by a pair of contact holes that are arranged to provide a series connection. Each of these contact holes can fully be formed by dry etching or, if not, the distance or the hole depth which has to be processed by wet etching can be minimized. It will be understood that the present invention makes it possible to reduce the diameter of each of the contact holes. This correspondingly reduces dimensions of dents and steps which appear on the surface of the conductive layer at the location right above the contact hole. This contributes to planarization of the corresponding portion of the overlying pixel electrode. Further, the dents and steps appearing on the surface of the pixel electrode at the location right above the contact hole can also be reduced, contributing to the planarization of the pixel electrode at this position.
The second contact hole is spaced apart from the pixel electrode by the intervening conductive layers and inter-layer insulating films, so that the influence produced by the second contact hole on the surface state of the pixel electrode is not so critical as compared with the influence produced by the first contact hole. It is, however, conceivable that dents and steps caused by the presence of the second contact hole produces a certain undesirable effect such as generation of disclination of the electro-optical substance, due to reasons attributable to the specifications of the device (required image quality) and the device design requirement (position of the second contact hole and distance of the second contact hole from the pixel aperture). In some cases, it may be desirable to omit planarization treatment on the region corresponding to the second contact hole. Under this circumstance, in accordance with the described feature of the invention, the second contact hole is formed within the non-aperture region at a position symmetrical with respect to two adjacent data lines. This arrangement, as in the case of the first contact hole, prevents the dents and steps appearing on the surface of the pixel electrode corresponding to the first contact hole in each pixel from deviating in either direction along the scanning line, thus avoiding generation of display unevenness having directivity along the scanning lines over the entire image display area.
In accordance with the present invention, a storage capacitor is added to the pixel electrode, and the conductive layer, a first inter-layer insulating film, the data line, a second inter-layer insulating film, and the pixel electrode are laminated in this order on the scanning line and one of the electrodes of the storage capacitor, the conductive layer and the pixel electrode being electrically connected to each other through the first contact hole formed in the first and second inter-layer insulating films.
With this arrangement, the connection between the semiconductor layer and the data line is achieved through the intermediary of the conductive layer, whereby the electrical connection is obtained between the conductive layer and the pixel electrode via the first contact hole. The first contact hole can be located anywhere on the planar region except the region where the data lines exist, thus enhancing the degree of freedom of the design.
In accordance with the present invention, a first insulating thin film constituting a first dielectric film is provided between a first storage capacitor electrode constituted by the same film as the semiconductor layer and a second storage capacitor electrode which constitutes the one of the electrodes of the storage capacitor, and a second insulating thin film constituting a second dielectric film is provided between the second storage capacitor electrode and a third storage capacitor electrode constituted by part of the conductive layer.
With these features, the first insulating thin film is provided between the first storage capacitor electrode constituted by the same film as the semiconductor layer and the second storage capacitor electrode which constitutes the one of the electrodes of the storage capacitor, and the second insulating thin film is provided between the second storage capacitor electrode and the third storage capacitor electrode constituted by part of the conductive layer. Therefore, a first storage capacitor and a second storage capacitor, that are coupled in parallel, are formed on upper and lower sides of the conductive layer. It is therefore possible to enhance the storage capacitor by three-dimensionally using the conductive layer within a limited region on the substrate.
In accordance with the present invention, a storage capacitor is added to the pixel electrode, and a first inter-layer insulating film, the data line, the conductive layer, a second inter-layer insulating film, and the pixel electrode are laminated in this order on the scanning line and one of the electrodes of the storage capacitor, the conductive layer and the pixel electrode being electrically connected to each other through the first contact hole formed in the second inter-layer insulating film.
With this arrangement, the connection between the semiconductor layer and the data line is achieved through the intermediary of the conductive layer, whereby the electrical connection is obtained between the conductive layer and the pixel electrode via the first contact hole. The first contact hole can be located anywhere on the planar region except the region where the data lines exist, thus enhancing the degree of freedom of the design. Further, it is possible to simultaneously form the conductive layer and the data lines. This means that the data lines can be formed without increasing the number of the process steps. When the data lines are formed of Al films, there is a risk that the connections between these data lines and the ITO films constituting the pixel electrodes may be impaired. To obviate this problem, the conductive layer may be formed to have two or more layers.
In accordance with the present invention, a storage capacitor is added to the pixel electrode, and a first dielectric film is provided between a first storage capacitor electrode constituted by the same film as the semiconductor layer and a second storage capacitor electrode which constitutes the one of the electrodes of the storage capacitor, and the first inter-layer insulating film constituting a second dielectric film is provided between the second storage capacitor electrode and a third storage capacitor electrode constituted by part of the conductive layer.
With these features, a first dielectric film is provided between a first storage capacitor electrode constituted by the same film as the semiconductor layer and a second storage capacitor electrode, and the first inter-layer insulating film constituting a second dielectric film is provided between the second storage capacitor electrode and a third storage capacitor electrode constituted by part of the conductive layer. Therefore, a first storage capacitor and a second storage capacitor, that are coupled in parallel, are formed on upper and lower sides of the conductive layer. It is therefore possible to enhance the storage capacitor by three-dimensionally using the conductive layer within a limited region on the substrate.
In accordance with the present invention, the scanning line and the second storage capacitor electrode are arranged substantially side-by-side when viewed in plan, and a second contact hole for providing electrical connection between the semiconductor layer and the conductive layer is formed at a position which is between the scanning line and the second storage capacitor electrode when viewed in plan.
This arrangement serves to prevent short-circuiting between the scanning lines and the second storage capacitor electrode, and the conductive layer which is electrically connected to the drain region of the semiconductor layer. The second contact hole leads to the semiconductor layer and, hence, cannot be positioned to overlap the scanning lines and the second storage capacitor electrode when viewed in plan. In accordance with the described feature of the present invention, the second contact hole is formed at a position between the scanning line and the second storage capacitor electrode when viewed in plan, whereby the above-mentioned short-circuit is prevented. In addition, dents and steps on the surface of the pixel electrode above the second contact hole due to the presence of this second contact hole are concentrated to a central portion between the scanning line and the capacitor line. Consequently, the dents and steps of the surface of the pixel electrode attributable to the presence of the second contact hole can be retracted apart from the aperture region of the pixel into the non-aperture region. Consequently, the dents and steps caused by the presence of the contact hole can hardly affect the aperture region, even when no planarization treatment is effected on the intervening layers such as the interlayer insulating films.
In accordance with the present invention, the scanning line and the second storage capacitor electrode are arranged substantially side-by-side when viewed in plan, and a second contact hole for providing electrical connection between the semiconductor layer and the conductive layer is formed at a position on the second storage capacitor electrode adjacent to the aperture region of the pixel when viewed in plan.
With these features, the second contact hole is formed at a position on the second storage capacitor electrode adjacent to the aperture region of the pixel when viewed in plan. The second contact hole reaches the semiconductor layer of the thin film transistor and, therefore, cannot be formed at a position where it overlaps the scanning line and the second storage capacitor electrode when viewed in plan. Namely, if such an overlap is allowed, the scanning line and the second storage capacitor electrode may be short-circuited to the conductive layer via the second contact hole. In accordance with the present invention, however, the risk of short-circuiting between the scanning line and the conductive layer, which is critical in the electro-optical device, is minimized, because the second contact hole is formed on the region of the second storage capacitor electrode adjacent to the pixel aperture when viewed in plan. Unlike the first contact hole, the second contact hole is spaced apart from the electrode, by a plurality of intervening layers such as the conductive layer and inter-layer insulating films. Therefore, the dents and steps appearing transferred from the second contact hole through the intervening layers to appear on the pixel electrode surface are inherently rather small. In case of the first contact hole, dents and steps are substantially inevitably formed to appear on the pixel electrode surface, and planarization to remove such dents and steps is extremely difficult. In contrast, the dents and steps attributable to the second contact hole can be removed to allow planarization relatively easily, through the intervening layers that intervene between the second contact hole and the pixel electrode. Therefore, by planarizing the inter-layer insulating films above the second contact hole as required, it is possible to reduce the risk of short-circuiting between the scanning line and the conductive layer attributable to the presence of the second contact hole, when the first contact hole is located, as described above, on the side of the second storage capacitor electrode contacting the aperture region, i.e., at a position near the aperture region of each pixel, when viewed in plan. In accordance with the present invention, wherein at least one of the first and second contact holes is arranged in plural for each of the pixels.
Provision of a plurality of contact holes effectively reduces the diameter of each contact hole for obtaining the same electrical conduction. Consequently, the sizes of the dents and steps appearing on the pixel electrode surface due to the presence of such contact holes can advantageously be reduced. Further, a redundant structure can be implemented by the plural contact holes, thus reducing the ratio of production of defective products.
In accordance with the present invention, the first contact hole is disposed substantially midst the width between the scanning line and the second storage capacitor electrode when viewed in plan.
With this feature, the first contact hole is disposed substantially midst the width between the scanning line and the second storage capacitor electrode when viewed in plan. Therefore, the dents and steps appearing on the pixel electrode surface due to the presence of the first contact hole are concentrated to the widthwise central portion of the non-aperture region extending along the scanning line. Consequently, the dents and steps due to the presence of the first contact hole becomes less likely to affect the pixel aperture region. Thus, in this embodiment, the requirement for the contact hole being located midst is sufficiently met if the contact hole is retracted into the non-aperture region away from the aperture region to such an extent that the undesirable effect on the aperture region caused by the dents and steps attributable to the second contact hole is substantially reduced.
In accordance with the present invention, the first contact hole and the second contact hole are arranged to overlap at least partially when viewed in plan.
With this arrangement, since the first contact hole and the second contact hole are arranged to overlap at least partially, it is possible to obtain symmetry of the pixel. In addition, the steps formed due to the presence of the contact holes can be concentrated to a certain area, whereby generation of disclination in the electro-optical material such as liquid crystal can be suppressed.
In accordance with the present invention, the aforesaid one of the electrodes of the storage capacitor is a capacitance line to which a predetermined potential is applied.
This arrangement serves to maintain the potential of the capacitance line at a constant level, thus stabilizing the potential of the second storage capacity.
In accordance with the present invention, the conductive layer is arranged to be substantially in symmetry with respect to the central axis line of the region between adjacent data lines.
This arrangement eliminates any deviation of the dents and steps appearing on each pixel surface, thus preventing generation of display unevenness over the entire image display area.
In accordance with the present invention, at least one of the first and second interlayer insulating film is recessed at least at a portion confronting part of the data line, or at least one of the first and second inter-layer has been subjected to a planarizing treatment so as to planarize the surface of the pixel electrode.
This effectively reduces the height difference between the region having the thin film transistor, scanning line, second storage capacitor electrode and so forth formed above the data line and other region. Thus, at least one of the first and second inter-layer insulating films is planarized at its surface facing the pixel electrode, including the portion confronting the first contact hole, by a suitable technique such as CMP (Chemical Mechanical Polishing), spin-coat processing or reflow processing, while using an organic SOG (Spin On Glass) film, inorganic SOG film, polyimide film or the like. Alternatively, at least one of the first and second inter-layer insulating film is recessed. By using one of these measures, the surface of the undercoating layer beneath the pixel electrode is planarized, thus allowing further planarization of the pixel electrode. This effectively suppresses undesirable effect such as generation of disclination in the electro-optical material such as liquid crystal attributable to dents and steps on the pixel electrode surface, thus leading finally to high quality of displayed images.
In accordance with the present invention, the conductive layer is formed from a conductive light-shielding film.
With this arrangement, the conductive layer made of a conductive light-shielding film can define the aperture region of each pixel at least partially. In this form of the invention, the light shielding film does not require a light-shielding film formed on the counter substrate which opposes the TFT array substrate. Rather, part or the entirety of the conductive light-shielding film is formed on the TFT array substrate itself. This arrangement is highly advantageous because it does not incur any reduction in the pixel aperture ratio which otherwise may be caused due to misalignment between the TFT array substrate and the counter substrate during the production process.
In accordance with the invention, the conductive layer may be arranged to define at least part of the aperture region of the pixel.
This arrangement makes it possible to define the pixel aperture region by the conductive film alone or in cooperation with a light-shielding film or the like formed on the counter substrate. Defining the aperture region without the aid of a light-shielding film formed on the counter substrate serves to reduce the number of the production process steps, and advantageously reduce the reduction and fluctuation of the aperture ratio attributable to misalignment between the pair of substrates.
In accordance with the present invention, the conductive layer is formed of a conductive polysilicon film.
With this feature, the conductive layer formed of the conductive polysilicon layer satisfactorily plays the role of the intermediary for the electrical connection between the pixel electrode and the drain region of the semiconductor layer, although it does not function as a light-shielding film. In particular, this feature suppresses generation of thermal stress at the interface between the conductive layer and the inter-layer insulating film, thus suppressing cracking of the conductive layer and other portions therearound.
In accordance with the present invention, the conductive layer has a laminate film having at least two layers including a conductive silicon film and a high-melt-point metal.
With this feature, the conductive layer formed of the conductive polysilicon layer satisfactorily plays the role of the intermediary for the electrical connection between the pixel electrode and the drain region of the semiconductor layer, although it does not function as a light-shielding film. Further, the use of conductive silicon as the material of the conductive layer remarkably reduces the contact resistance at the point of connection between the conductive layer and the semiconductor layer when the semiconductor layer is formed of the same polysilicon film. Lamination of a high-melt-point metal on this conductive polysilicon layer serves to further reduce the resistance, while ensuring a light-shielding function.
In order to overcome the aforesaid problems, in accordance with the present invention, there is provided a method of producing an electro-optical device of the type having a plurality of scanning lines, a plurality of data lines, thin-film transistors and pixel electrodes arranged at positions corresponding to the points where the scanning lines and data lines cross each other, and at least one conductive layer electrically connected between a semiconductor layer constituting the thin-film transistor and the pixel electrode, the method may consist of the steps of: forming the semiconductor layer on a substrate; forming a first insulating thin film on the semiconductor layer; forming the scanning lines on the first insulating thin film; forming a second insulating thin film on the scanning lines; forming a conductive layer on the second insulating thin film; forming a first inter-layer insulating film on the conductive layer, forming the data lines on the first inter-layer insulating film; forming a second inter-layer insulating film on the data lines; forming the first contact hole in the second inter-layer insulating film at a position substantially symmetrical with respect to two adjacent data lines; and forming the pixel electrode such that electrical connection is achieved between the pixel electrode and the conductive layer via the first contact hole.
The method having these features makes it possible to produce the described first aspect of the electro-optical device of the present invention with fewer and simpler production process steps.
In order to overcome the aforesaid problems, the present invention also provides a method of producing an electro-optical device of the type having a plurality of scanning lines, a plurality of data lines, thin-film transistors and pixel electrodes arranged at positions corresponding to the points where the scanning lines and data lines cross each other, and at least one conductive layer electrically connected between a semiconductor layer constituting the thin-film transistor and the pixel electrode; the method may consist of the steps of: forming the semiconductor layer on a substrate; forming an insulating thin film on the semiconductor layer; forming the scanning lines on the insulating thin film; forming a first inter-layer insulating film on the scanning lines; forming the data lines and the conductive layer on the first inter-layer insulating film; forming a second inter-layer insulating film on the conductive layer; forming the first contact hole in the second interlayer insulating film at a position substantially symmetrical with respect to two adjacent data lines; and forming the pixel electrode such that electrical connection is achieved between the pixel electrode and the conductive layer via the first contact hole.
The method having these features makes it possible to produce the electro-optical device of the present invention with fewer and simpler production process steps.
In accordance with the present invention, the step of forming the scanning lines includes a step of forming one of the electrodes of a storage capacitor added to the pixel electrode, so as to extend along and in side-by-side relation to the scanning line from the same material simultaneously with the formation of the scanning line, the method further may consist of the step of forming a second contact hole at a position between the one of the electrodes of the storage capacitor and the scanning line when viewed in plan.
With these features, it possible to produce the electro-optical device of the present invention with fewer and simpler production process steps.
The above and other operations and advantages of the present invention will become clear from the following description of the preferred embodiments.